Consumption of sugar sweetened beverages (SSB) has been linked to obesity and, independent of body weight, risk for diabetes and cardiovascular disease. With rising public health awareness of these potential adverse effects, consumption of artificially sweetened beverages (ASB) has increased dramatically. These low-calorie products are marketed as diet, with the implication that they promote weight loss and improved health. However, there are no long term experimental studies of ASB and body weight or any other health outcome. Several recent prospective observational studies have linked intake of ASB to increased risk of the metabolic syndrome, type 2 diabetes, and obesity. In the proposed clinical trial, 270 young adults who habitually consume SSB will be randomly assigned to one of three groups: 1) to continue consuming habitual levels of SSB; 2) to substitute ASB for SSB; or 3) to substitute unsweetened beverages for SSB. Each group will receive home delivery of the targeted beverage for 1 year, using methods that build upon previous successful work. Careful attention will be given to assuring treatment fidelity, equivalence of treatment intensity, and avoidance of experimental confounders. The primary study endpoint will be the ratio of serum triglyceride to HDL-cholesterol concentrations. Secondary endpoints will include changes in other cardiovascular disease risk factors, body weight, dietary quality, and taste preferences.